52 S. P. Langley — Internal Work of the Wind. 



flow ; for, while if we consider air as an absolutely elastic and 

 frictionless fluid, any motion impressed upon it would be pre- 

 served forever, and the actual irregularities of the wind would 

 be the results of changes made at any past time, however 

 remote ; so long as we admit that the wind without being 

 absolutely elastic and frictionless, is nearly so, it seems to me 

 that we may consider that the incessant alternations which it 

 here appears make the "wind," are due to past impluses and 

 changes which are preserved in it, and which die away with 

 very considerable slowness. If this be the case, it is less diffi- 

 cult to see how even in the upper air, and at every altitude, we 

 might expect to find local variations, or pulsations, not unlike 

 those which we certainly observe at minor altitudes above the 

 ground.* 



Part III. — Application. 



Of these irregular movements of the wind, which take place 

 up, down, and on every side, and are accompanied of neces- 

 sity by equally complex condensations and expansions, it will 

 be observed that only a small portion, namely, those which 

 occur in a narrow current whose direction is horizontal and 

 sensibly linear, and whose width is only the diameter of the 

 anemometer, can be noted by the instruments I have here 

 described, and whose records alone are represented in the dia- 

 gram. However complex the movement may appear as shown 

 by the diagram, it is then far less so than the reality, and it is 

 probable indeed, that anything like a fairly complete graphi- 

 cal presentation of the case is impossible. 



I think that on considering these striking curves (Plates I, II, 

 III, IV and Y) we shall not find, it difficult to admit, at least as 

 an abstract conception, that there is no necessary violation of the 

 principle of the conservation of energy, implied in the admis- 

 sion that a body wholly immersed in and moving with such a 

 wind, may derive from it a force which may be utilized in 

 lifting the body, in a way in which a body immersed in the 

 " wind " of our ordinary conception could not be lifted, and if 

 we admit that the bod} 7 may be lifted, it follows obviously 

 that it may descend under the action of gravity from the 

 elevated position, on a sloping path, to some distance in a 

 direction opposed to that of the wind which lifted it, though 

 it is not obvious what this distance is. 



We may admit all this, because we now see (I repeat) that 

 the apparent violation of law arises from a tacit assumption 

 which we in common with all others, may have made, that the 



* In this connection, reference may be made to the notable investigations of 

 HelmhoJtz, on Atmospheric Movements, Sitzungsberichte, Berlin, 1888-1889. 



